The present invention generally relates to a filling apparatus provided with a filling amount weighing apparatus, and more particularly, to an apparatus which is used in a process of preparing medical supplies and so on, and continuously automatically fills powder, liquid or the like of a very small amount such as 50 mg, 100 mg, 500 mg, 1,000 mg or the like into a container such as a vial, ampoule or the like so as to weigh the filling amount and also automatically controls a filling machine. The present invention uses an electronic balance as the weighing apparatus to effect a weighing operation at high speed and precision so as to improve the filling amount accuracy through a reduction in variation in the filling amount. The filling machine is controlled through the feedback-control of the weighing value to effect quantitative control of the filling amount. Furthermore, the apparatus is provided with means for effecting an emergency stop when clogging occurs.
Conventionally, in a process of filling medicine of this kind, the inspection of the filling amount is executed generally by methods (1) and (2) described hereinafter.
(1) A container filled with powder, liquid or the like is manually taken out of the conveying line so as to weigh it on a balance disposed at an off-line position. Thereafter, the contents (powder or the like) are discharged and the empty container is weighed and the filling amount is calculated by substraction.
(2) When an automatic discharged weighing apparatus has been disposed on the production line, an empty container which is not filled is drawn out properly for the weighing operation. After the filling operation, it is drawn out again for the weighing operation. The filling amount is calculated by subtraction.
When there is a difference between the calculated filling amount and the target amount in either of the above-described methods (1) and (2), a proper adjustment of the filling amount is executed.
Generally, in the powder filling system, the filling amount varies due to changes in the hopper level (stock amount) of the bulk material, specific volume, properties of the material and so on. Also, in the filling of liquid (including a suspension agent) or the like, the filling amount varies due to changes in viscosity, clogging of the needle point filter, looseness of the cylinders or the like. Thus, it is necessary to check the above-described filling amount at proper frequencies and to adjust the filling amount. However, in the filling process, abnormal changes in the filling amount may be caused because of unexpected problems in addition to the above-described normally expected changes. The conventional proper sampling inspections cannot check the abnormal filling amount due to unexpected trouble. When handling medicine, the conventional sampling weighing operation cannot cope with variations in filling amount because the accuracy of the filling amount must remain extremely high and also, defective products must not be produced under any circumstances.
Although weighing operations for weighing the respective filling amount for all the containers may overcome the above-described problem, the weighing operations for all the containers are hard to effect in the conventional weighing apparatus, because productivity is extremely reduced due to the weighing speed being slower than the filling speed.
Also, in order to weigh a very small amount by the use of an electronic balance, conventionally there is a method of obtaining a weighing value (a balance reference stability detecting method) through an averaging operation with a constant time averaged, conventionally in a stable output mode with a constant number of data being included within the tolerance width, a method of effecting a sampling operation after the passage of a set period of time, and other methods.
The method of obtaining the weighing value by the above-described stable output mode has a disadvantage in that generally too much time is taken to effect the high-speed weighing operation when high accuracy is required. If the tolerance width is widened to shorten the time, the accuracy becomes worse. In a method of effecting a sampling operation after the passage of the given period of time, the accuracy becomes worse if the established time is shortened. Also, more time is taken if the established time is lengthened to improve accuracy, and unexpected inferior data may be included because of noise, vibrations and so on.
Furthermore, when a measurement of extremely high accuracy such as approximately 1 mg or lower is effected, magnetic force lines or the like caused by temperature changes, the controller and the like, have a negative influence upon the measurement accuracy. Especially, the negative influence caused by static electricity cannot be avoided even if an electronic balance is provided in an evacuated enclosure such as is used conventionally, thus reducing the measurement accuracy of the electronic balance.
In this type of powder filling apparatus, when the filling into a certain number of sequential containers is continuously effected by the driving of the filling machine after a given amount of material is supplied into the hopper of the filling machine, the tendency of the filling amount to fluctuate is great in addition to the variation of the filling amount in the initial mode at the start of the operation of the filling machine. Also, even in the final mode when the amount of material in the hopper becomes smaller, the tendency of the filling amount to fluctuate becomes great. Although the least variation in the filling amount occurs in a steady operating state between the initial mode and the final mode, there is a tendency for the filling amount to fluctuate in a gradually increasing or decreasing manner. The above-described characteristics of the variation and the fluctuating tendency of the filling amount occur in accordance with the duration of the operation of the filling machine. Although the control is good when the filling amount is stable in a case where feedback control operation is effected based on the average value of a few filling amount data during an all container weighing operation, even if a uniform feedback control is effected from starting time to stopping time, there is a disadvantage in that the feedback cannot follow the tendency of the weighing amount to fluctuate sufficiently in the initial mode and the final mode during which the fluctuating tendency is greater. When the feedback controlling operation has been effected one by one to follow the variation in the filling amount of the final mode at the initial stage, one unexpected bad datum in the stable period of the steady mode of operation may be picked up. Even if all the container weighing operations are effected in this manner, there is a problem as to how the feedback controlling operation may be effected in accordance with the weighing results.